None.
Not Applicable.
The present invention is directed to particle sorting in an apparatus for grinding fuel or other material prior to its delivery to a boiler or other point of use, and in particular, to an improvement for equalizing gas velocity around large roller grinder journals to reduce vertical cycling of larger particles and to function as a first stage separator, returning and directing larger particles to the roller grinders for further reduction.
In the processing of particulate material, like coal, rock, and similar particulates that require reduction in the size of particles prior to processing, isokinetic separator apparatus such as is shown in U.S. Pat. No. 5,279,466 to Williams, herein incorporated by reference, are known. The ""466 Williams patent discloses an apparatus for grinding material consisting of both desirable fines and undesirable oversize particles, in which a separator rotor is equipped with shaped blades to isokinetically separate out the oversize particles and return them to a grinder for further reduction.
The design of these grinders conventionally includes either a hammer mill or a roller mill such as is disclosed in U.S. Pat. No. 4,522,343 to Williams, herein incorporated by reference. The ""343 Williams patent discloses an apparatus for grinding coal to micron fineness having a grinding chamber with a grinding surface supported by a circumferential wall in the grinding chamber and four grinding rolls orbiting in the grinding chamber for grinding the coal between the roller surface and the grinding surface. Typically, the inner diameter of the grinding surface in conventional grinding mills is approximately 74 inches across. Scaled up designs for larger grinding mills, having an inner grinding surface diameter of approximately 100 inches, and more than 4 grinding rollers have been attempted. However, it has been found that use of additional grinding rollers reduces the cross-sectional area through which particulate material can pass in a vertical direction between the grinding rollers and the grinding mill journal, resulting in an increase in the velocity of the fluidizing gasses passing therethrough. The increased velocity of the fluidizing gasses forces larger particles up out of the grinding chamber, and into the particle separator area, wherein they are rejected and returned to the grinding chamber. Due to the increased velocity of the fluidizing gasses, the rejected particles are again ejected from the grinding chamber, cycling between the particle separator and the grinding chamber, resulting in an increase in power consumption by the grinding mill, separator and air system that must support the fluidized accumulation.
Briefly stated, the present invention is an improvement to the conventional grinding mill and separator designs which facilitates the use of larger diameter grinding surfaces and additional numbers of grinding rollers by equalizing the gas velocity around the grinding rollers and journal with the gas velocity employed to fluidize the particulate material. Specifically, in a preferred embodiment, a plurality of peripheral vertical staticseparators are located above the grinding chamber and grinding rollers to provide an increase in the cross-sectional area of the grinding mill, thereby reducing the gas velocity around the grinding rollers and journal. In addition to increasing the cross-sectional area of the grinding mill, the vertical static separators are configured with a trapezoidal sectional area, such that oversize particulate material falling or flung by the rotating journals into the vertical static separator is redirected down into the grinding chamber, resulting in an increase in the number of grinding chamber material introduction points. Finally, the centrifugal action of the grinding journal ejects oversize particulate material directly into the peripheral vertical static separators before it reaches the spinner separator, thereby allowing the vertical static separator to function as a first stage separator and permitting the spinner separator chamber to be run at a slower speed, reducing power consumption of the separator and primary fluidizing fan.
The foregoing and other objects, features, and advantages of the invention as well as presently preferred embodiments thereof will become more apparent from the reading of the following description in connection with the accompanying drawings.